RF MEMS switches have previously been employed in microwave and millimeter-wave communication systems, such as in signal routing for transmit and receive applications, switched-line phase shifters for phased array antennas, and wide-band tuning networks for modern communication systems. In particular, RF MEMS switches (e.g., single-pole multi-throw switches) and switching networks are broadly used in modern telecommunication systems, especially for 2G/3G/4G applications and high precision instrumentation.
FIG. 1 illustrates the circuit design of a basic single pole single throw (SPST) lateral RF MEMS switch 100. As shown in FIG. 1, the lateral switch includes a coplanar waveguide 101, a cantilever beam 140 extending between first and second ports 110, 120 of the coplanar waveguide, and an electrostatic actuator (not shown) for actuating the cantilever beam. The actuator is configured to apply a DC bias voltage between the cantilever and the ground line 130 of the coplanar waveguide 101, thereby causing the free end of the cantilever beam 140 to deflect in the direction of a fixed electrode 125. When sufficient DC bias is applied, the cantilever beam 140 deflects enough to contact a mechanical stopper of the second port, resulting in the closing (ON state) of the switch. When the DC bias is lowered or removed, the beam 140 returns to its at-rest state (as shown in FIG. 1), thereby opening the switch (OFF state).
Compared to PIN diodes or field-effect transistor (FET) switches, RF MEMS switches have been found to offer lower power consumption, higher isolation, lower insertion loss, higher linearity, and lower cost.
One drawback of the lateral switch design is that it is prone to electromechanical failure after several switching cycles, especially under hot switching conditions. For instance, the switch may fail due to static friction (or stiction) buildup between the cantilever beam and the mechanical stopper of the waveguide port. Furthermore, the spring constant of the cantilever beam is often too small to overcome the stiction. Another drawback of the lateral switch design is that, with a large number of output ports, they do not achieve a wide band performance with good repeatability, especially at lower microwave frequencies such as about 20 GHz. At lower microwave frequencies, area also plays a major role in the performance of the switch. Isolation and matching also play key roles in the switch, and the effect of isolation degrades gradually with higher number of output ports.
Therefore, there is a need to address these and other drawbacks in the field of MEMS switch design.